Cylindrical magnetron target and apparatus for affixing the target to a rotatable spindle assembly

ABSTRACT

An improved interconnection system for attaching an improved cylindrical magnetron target to a rotatable flanged spindle incorporates an annular extension on the target, which fits over the edge of the spindle flange, facilitates centering the target on the spindle, and helps shield target sealing surfaces. The annular extension terminates in an inwardly-angled circumferential step. The target-spindle interconnection system includes a split clamping collar and generally annular retainer ring that slidable over the spindle shaft and rotatable against the spindle flange, the retainer ring having external circumferential threads that are angled away from the flange. The split clamping collar has, at one end, an inwardly-angled lip that engages the overhanging step and, at the other end, inwardly-angled, internal, circumferential threads that engage the threads of the retainer ring to draw the target and spindle together as a unified assembly as the retainer ring is rotated.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to equipment employed for the coatingof substrate articles by magnetron sputtering and, more specifically, tothe design of rotatable targets and target mounting spindles used bysuch equipment, as well as methods and apparatus for affixing suchtargets to a target mounting spindle.

2. Description of the Prior Art

For at least several decades, sputtering has been the dominant processfor the deposition of thin coatings on large-surface-area substrates,such as architectural glass panels, automobile windshields, and thelike. The coating materials are deposited with a magnetron in a vacuumchamber containing a reactive gas. Although planar magnetrons were usedinitially for sputtering processes, rotating cylindrical magnetrons havenow come into wide use. This is because cylindrical magnetrons, thoughmore complex than their planar counterparts, typically feature higherdeposition rates, higher material utilization per cathode target, lowermaintenance frequency, and greater cost efficiency. Another majoradvantage of using a rotating cylindrical target, as opposed to a planartarget, is that dielectric silicon compounds, such as silicon nitrideand silicon dioxide, can be sputtered with ease. Such compounds areextremely difficult to sputter using a planar target.

Various mechanisms for supporting, rotating, cooling and energizing acylindrical target structure in a magnetron, are described in U.S. Pat.No. 5,096,562 to Boozenny, et al. The structure employs a removablesupport spindle at each end of the cylindrical target structure. A firstsupport spindle at one end supplies and withdraws cooling fluid fromwithin the cylinder and contains a driving mechanism to rotate it, whilea second support spindle at the other end contains the electrical powerconnection to the target surface.

An improved apparatus to releasably affix a rotatable cylindricalmagnetron target to a support spindle is disclosed in U.S. Pat. No.5,591,314 to Morgan, et al. The inventors claim that a primarydisadvantage of the Boozenny, et al. design is frequent breakdownscaused by coolant leaks at the interface between the first supportspindle and the cylindrical target structure. The leaks are due to thefact that one side of any seal at the spindle-to-target interface issubjected to the low pressure present within the deposition chamber,while the other side of the seal is subjected to high coolant pressure.The Morgan, et al. apparatus supposedly improves on the Boozenny, et al.apparatus by providing a removable coiled wire thread connection system,by employing a single coolant seal ring, to which uniform pressure isapplied as the target is attached to the support spindle. For apreferred embodiment, the target, the spindle, and the coiled wirethread are made from dissimilar materials.

Though the Morgan, et al. apparatus seems to be a significantimprovement over the Boozenny, et al. apparatus, there are severaldisadvantages associated with the design of the former. Firstly, the useof the coiled wire thread requires that a spiral groove be machined inthe cylindrical target body, thereby weakening the structure. Thethickness of the target cylinder at the deepest point of the groove isonly about 1.0 millimeter (0.030 inch). Secondly, the target bodysealing surface is on a circumferential edge thereof. As the edge haslittle surface area, it is easily nicked. Nicks in the sealing surfacemay well cause coolant leaks. Thirdly, the coupling arrangement betweentarget and spindle does not permit the transfer of large torque loads.Fourthly, the threaded coupling arrangement does not lend itself toevenly distributed clamping forces between the target and the spindle.

What is needed is are new cylindrical target and spindle designs whicheliminate the disadvantages of the prior art targets and spindles.

SUMMARY OF THE INVENTION

The present invention includes a method and apparatus for attaching arotating cylindrical magnetron target to an existing, rotatable flangedsupport spindle. Several design improvements have been incorporated intothe magnetron target, and the attachment apparatus is specificallydesigned to couple the improved magnetron target to the support spindle.The objectives in creating the improved magnetron target and attachmentapparatus were to improve the reliability of a rotating cylindricalmagnetron cathode, decrease the time required to change out an installedtarget, decrease the likelihood of coolant leaks by providing a targetthat is less likely to become marred or nicked on the sealing surface,improve the structural integrity of the target, and provide atarget-spindle unifying clamp system which provides more evendistribution of clamping pressure, thereby permitting the transfer ofmuch larger torque loads from the spindle to the target.

The improved target includes a circumferential lip, which fits over thespindle's outer mating circumferential edge. This lip affords additionalprotection to a circumferential sealing surface on the target, so thatit is less likely to become mechanically damaged. The circumferentiallip extends from a circumferential shoulder that terminates in acircumferential, inwardly-angled, overhanging step. The target andspindle are coupled together with an generally annular retainer ringhaving external, outwardly-facing circumferential threads, and a splitclamping collar having an inwardly-angled clamping ledge at one endthereof that mates with the overhanging circumferential step on thetarget, and internal, inwardly-facing circumferential threads at theother end, which mate with the external threads of the retainer ring.The retainer ring is rotated with a spanner wrench so as to engage thethreads of the split clamping collar. As the retainer ring engages therear face of the spindle flange, the clamping collar and retainer ringact in concert to draw the target and spindle together as a unifiedassembly. As the target and spindle are drawn together, thecircumferential sealing edge of the target compresses an O-ring seal setwithin an annular groove in the spindle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an improved magnetron targetseparated from a rotatable support spindle;

FIG. 2 is a cross-sectional view of the improved magnetron target andspindle of FIG. 1, having been joined with a unique attachment apparatusthat includes an internally-threaded split collar and anexternally-threaded retainer ring;

FIG. 3 is a rear elevational view of the retainer ring;

FIG. 4 is a side elevational view of the retainer ring;

FIG. 5 is a front elevational view of the two-piece split collar;

FIG. 6 is a side elevational view of the interior of a first half of thesplit collar;

FIG. 7 is a side elevational view of the interior of the second half ofthe split collar; and

FIG. 8 is an exploded view of the improved target, the spindle and theattachment apparatus components.

PREFERRED EMBODIMENT OF THE INVENTION

The present invention includes an improved magnetron target and anapparatus and method for attaching the improved target to a rotatablesupport spindle. The target, attachment apparatus and method of usingthe apparatus will now be described in detail with reference to theattached drawing FIGS. 1 through 8.

Referring now to FIG. 1, a rotatable support spindle 100 and theimproved magnetron target are aligned for assembly into a single unit.The support spindle 100, which is generally radially symmetrical aboutaxis 101, includes a circumferential flange 102 at a target attachmentend thereof, said flange having both a rear face 103 and a front face104. The front face 104 of flange 102 incorporates a circumferentialgroove 105 in which is inserted a compressible O-ring seal 106. It willbe noted that the support spindle 100 is equipped with axial aperture107, through which coolant fluid may be pumped into the target chamber201. The improved magnetron target 200, which is also radiallysymmetrical about axis 101, incorporates an circumferential lip 202 at aspindle attachment end thereof, said lip fitting over the front edge 108of the spindle flange 102. The lip 202 facilitates accurate axialpositioning of the target 200 on the support spindle 100, and alsoshields a circumferential sealing surface 203, which contacts O-ringseal 106, from mechanical damage in the form of scratches, nicks anddents. If the sealing surface 203 were to become damaged, the O-ring 106may not be able to effectively seal the joint between the supportspindle 100 and the target 200, when the two units are joined. The lip202 extends from a circumferential shoulder 204, which terminates in aninwardly-angled, overhanging circumferential step 205.

Referring now to FIG. 2, the support spindle 100 and the magnetrontarget 200 are shown as a unified assembly, being joined with theattachment apparatus of the present invention. The target-spindleattachment apparatus includes a retainer ring 206 and a split clampingcollar coaxial with the target 200, said collar consisting of a firsthalf collar 207A and a second half collar 207B. The retainer ring 206 issized so that it is slidable over the spindle shaft 108 so that it canaxially rotate against the rear face 103 of the spindle flange 102. Theretainer ring 206 incorporates external circumferential spiral threads208 of generally parallelogram cross section that are angled away fromthe spindle flange 102. The retainer ring 206 also incorporates aplurality of recesses 209 about its periphery, which can be engaged by aspanner wrench (not shown). The split damping collar 207A/207Bincorporates, at one end thereof, an inwardly-angled clamping ledge 210,that engages the overhanging circumferential step 205 of the target 200.The other end of the split clamping collar 207A/207B incorporatesinternal, inwardly-angled, spiral, circumferential threads 211, also ofgenerally parallelogram cross section, that engage the external threads208 of retainer ring 206 as the latter is rotated counterclockwise, asviewed toward the rear of spindle flange 102. As the retainer ring 206is further rotated, the retainer ring 206 eventually presses against therear face 103 of spindle flange 102, thereby drawing the clamping ledge210 of the split clamping collar 207A/207B toward the support spindle100, and clamping the support spindle 100 and the improved magnetrontarget 200 together as a unified assembly. The remaining drawingfigures, which more clearly show the various components, will clarifythe structure of the attachment apparatus and the implementationthereof.

Referring now to FIGS. 3 and 4, the structure of the retainer ring 206is shown in greater detail. The external threads 208 are of left-handedconfiguration because of the rotational direction employed for thesupport spindle 100. With threads of a left-handed configuration, theretainer ring 206 is deemed to be less likely to loosen as the unifiedsupport spindle 100 and magnetron target 200 assembly is accelerated tooperating rotational speeds.

Referring now to FIGS. 5, 6 and 7, the structure of the split clampingcollar 207A/207B is shown in greater detail. Though the clamping collarmight be configured as more than two arcuate segments, two 180-degreesegments are most convenient, as fewer parts must be retained in properposition during assembly. When the ends of clamping collar halves 207Aand 207B are mated together so that clamping ledge 210 of each isaligned, the internal threads 211 of one collar half 207A or 207B arecontinuous with those of the other collar half. In order to properlyinstall the clamping collar 207A/207B on the improved target 200, thetwo halves of the collar are slipped over the target 200 and, with thetarget 200 held against the face of spindle 100, the two collar halves207A/207B are slid toward the spindle until the clamping ledge 210engages the circumferential step 205 of the target 200. The retainerring 206 is then rotated counterclockwise until its external threads 208engage the internal threads of the split damping collar halves207A/207B. Further rotation of the retainer ring 206 eventually securesthe clamping collar halves 207A/207B and the engaged target 200 to thesupport spindle 100.

Referring now to FIG. 8, the entire support spindle/target assembly andattachment apparatus are shown in an exploded view. From this view andthe foregoing description and explanation, the function of the variouscomponents should be quite clear. It should also be evident that thedisclosed spindle attachment apparatus is capable of rapidly andeffectively coupling the improved target 200 to the support spindle 100.

Although only a single embodiment of the invention is shown anddescribed herein, it will be obvious to those having ordinary skill inthe art that changes and modifications may be made thereto withoutdeparting from the scope and the spirit of the invention as hereinafterclaimed.

What is claimed is:
 1. An apparatus for affixing a cylindrical magnetrontarget to a rotatable support spindle, said apparatus comprising: asupport spindle structure including a target attachment flange, saidtarget attachment flange having a rear face and front face whichincorporates a circumferential groove into which an O-ring seal isinserted; a cylindrical target structure having a circumferentialshoulder at a spindle attachment end thereof, said shoulder terminatingin an inwardly-angled, overhanging circumferential step that faces awayfrom said spindle attachment end; a clamping collar comprised of arcuatesegments, which are collectively sized to generally and coaxiallysurround said cylindrical target structure, said clamping collarincorporating, both an inwardly-angled clamping ledge that engages theoverhanging circumferential step of the cylindrical target structure andat least one internal, inwardly-angled, spiral, circumferential threadspaced apart from said inwardly-angled clamping ledge; and a retainerring sized so as to be slidable over the support spindle structure, androtatable against the rear face of the target attachment flange, saidretainer ring incorporating external, spiral, circumferential threadsthat are angled away from the spindle flange, the external, spiral,circumferential threads of said retainer ring engaging the at least oneinternal, inwardly-angled, spiral, circumferential thread of saidclamping collar to draw the inwardly-angled clamping ledge and engagedcylindrical target structure toward the target attachment flange as theretainer ring is rotated in a thread engaging direction.
 2. Theapparatus of claim 1, wherein the external, spiral, circumferentialthreads of said retainer ring and the at least one internal,inwardly-angled, spiral, circumferential thread of said clamping collarare generally of parallelogram cross section.
 3. The apparatus of claim1, wherein said clamping collar is comprised of a pair of generally180-degree arcuate segments.
 4. The apparatus of claim 1, wherein theexternal, spiral, circumferential threads of said retainer ring and theat least one internal, inwardly-angled, spiral, circumferential threadof said clamping collar are of a left-handed spiral configuration. 5.The apparatus of claim 1, wherein said cylindrical target structurefurther comprises a circumferential lip at a spindle attachment endthereof, said lip fitting over a front edge of said target attachmentflange.
 6. The apparatus of claim 1, wherein said retainer ring isequipped with a plurality of spanner wrench engagement recesses aboutits periphery.
 7. The apparatus of claim 1, wherein said cylindricaltarget structure further comprises an inner circumferential sealingsurface which mates with said O-ring seal.
 8. The apparatus of claim 7,wherein a circumferential lip is proximate said inner circumferentialsealing surface in order to afford the latter protection againstmechanical damage.